"Morse code" PCM transmissions from Soviet
reconnaissance satellites
Starting with Kosmos 251 a
new
type of transmission appeared consisting of 12 groups, each of 3 Morse
code characters. This signal was normally transmitted on 19.150 MHz,
but
sometimes appeared on 19.300 MHz (when there were two similar
satellites
in orbit ant the same time) and once on 19.995 MHz. Each group was
formed
of characters giving seven pulses per group in a 2-3-2 configuration
with
the exception of one 3-1-3 group which served to denote the start of
the
frame. These represented 7-bit pulse code modulation binary code with
the
most significant bit transmitted first. The sixth group , which was
always
MWI during the main part of the mission, changed to MRI on the day
prior
to recovery at the same time an additional piece was catalogued in
orbit.
The numerical value of the seventh group increased steadily during the
flight and was shown to be a film exposure counter. Click here
to listen to the signal
(68 kB
mp3-file).
Source: chapter 5
"Soviet
Military Space Activities" in "Soviet Space Programs: 1976-80, Part 3,
US Govt. Printing Office, May 1985.
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